1. Field of the Invention
The present invention relates to a seat back support structure and a seat for a vehicle for stably supporting a pelvis portion or a lumbar portion of a passenger so as to surely make the passenger comfortable to sit in a seat when the seat is in use.
2. Description of the Related Art
In a related art, there has been known a seat back support unit in an automobile seat or the like, which unit has a structure as follows. That is, the seat back support unit is provided inside a seat back in the state where a contour mat, a resin mat or the like is supported on a seat frame through springs. A back portion of a passenger sitting in the seat is supported by the mat. FIGS. 9 and 10 show such a background-art example. In FIGS. 9 and 10, the reference numeral 21 represents a sheet-like mat such as a contour mat or a resin mat; 22, a seat frame; 23, springs for linking/supporting the mat onto the seat frame; and 24, a rod stretched in an upper portion of the seat frame.
In such a seat, however, there occurs a phenomenon that the pressure to support a pelvis portion or a lumbar portion of a passenger sitting in the seat is weakened due to a large bending distance of the mat 21 in a portion abutting against the pelvis portion or the lumbar portion of the passenger as shown in FIG. 10. As a result, there is a problem that the passenger slouches to be uncomfortable or exhausted.
On the other hand, there has been also proposed a lumbar support unit intended to improve the rigidity of a lumbar portion so as to adjust the lumbar portion to a desired retention state, for example, as disclosed in JP-A-2001-292855. However, when such a lumbar support unit is attached, there occurs a problem that the number of parts increases and the structure is also complicated. Particularly there is another problem that the lumbar support unit is not suitable to a seat intended to be thin and light.